This invention relates to knife adjustment means and particularly such a construction utilized in combination with means for forming thermoplastic pellets wherein strands of thermoplastic material are extruded into an enclosed chamber whereupon they are cut into discrete particles or pellets by rotating knives. The invention is particularly directed to a novel adjustment mechanism for moving the knives towards and away from the face of the die in such a manner that the desired gap therebetween is substantially unaffected by temperature changes within the knife supporting structure.
Pelletizing apparatus including those having knife adjustment systems of this general type are known and include that shown in U.S. Application Ser. No. 748,235 filed Dec. 6, 1976, now U.S. Pat. No. 4,099,900, directed to a novel pellet cooling system and assigned to the assignee of the present invention. Such adjustment system and those systems similar thereto generally move that portion of the apparatus upon which the knives are supported freely towards and away from the normally heated face of the extrusion die from some adjustment point conveniently remote therefrom. Accordingly, when such adjustment is initially made as upon startup of the machine, heat buildup at those portions of the knife supporting structure proximal to the face of the heated die may expand at a different rate than portions thereof located more remote from the heat source and subsequently cause changes in the knife gap or spacing. Generally this change of spacing is away from the die face and requires an inward adjustment during operation which can as upon cooling during shut off cause a knife shift against the die and scoring of the die face upon a subsequent start up. Such mechanisms also require readjustment during operation.
Accordingly, it is a primary object of the present invention to provide a novel adjustment mechanism for an extrusion apparatus of the aforementioned type in which relative heat changes in the various areas thereof does not adversely affect the knife adjustment setting.
A further object of the present invention is the incorporation into such equipment of a novel knife adjustment mechanism such that adjustment thereof may take place at a convenient location distal from the operating extrusion die face and in such a manner that rotational operator adjustment movement is translated to similar movement relative to the die face.
A still further object of the present invention is the provision of a knife support and adjustment means wherein such is assembled with the extrusion die at a point proximate the heated face thereof whereby expansion movements between the die and knife support are equalized.